Is owning a full PA system really all that viable an option?
I wouldn't say so.
But I always stress in my rider what sort of PA and Video equipment I precise fro the show. It is a requirement (except on certain cases, I'm pretty lenient and consider the party and venue's limitations) to have good equipment and properly set up. This is not to be under looked, sometimes promoters hire the best equipment, but without an equally apt tech, they will be set up like shit.